Apparatus for supplying pulses of constant width to a load device



y 23, 1967 M. FELCHECK ETAL APPARATUS FOR SUPPLYING PULSES OF CONSTANTWIDTH TO A LOAD DEVICE I Filed July 14, 1964 INVENTQRS MARVIN- FELCHECKN. NARASIMHA MURTHY' United States Patent 3,321,674 APPARATUS FORSUPPLYING PULSES 0F CON- STANT WIDTH TO A LOAD DEVICE Marvin Felcheck,Bayside, N.Y., and Nanjundiah N.

Murthy, Norwalk, Conn., assignors to American Machine & Foundry Company,a corporation of New Jersey Filed July 14, 1964, Ser. No. 382,553 5Claims. (Cl. 317148.5)

This invention relates to circuits for providing an electrical pulse ofpredetermined duration, or a succession of pulses each of predeterminedduration, to a load device and, more particularly, to such systemscapable of operating from an unregulated voltage source.

In the design and construction of various automatic sysbems, includingcomputers, automatic machine tools and the like, it is frequentlydesirable to use electromagnetic relays of various types which requirepulses of a particular, predetermined duration for proper operation.Circuits have been designed to provide such fixed-width pulses, butthese circuits have generally required the use of power sources whichare closely regulated so that the time constants on which pulse durationdepends do not vary.

Relays in general are designed to operate within a specified range ofvoltages. Usually, a minimum energizing voltage or current is specifiedbelow which the device will not dependably function, and a maximum mayalso be specified above which the device may overheat or be otherwisedamaged. Within this range, the pulse duration should be constant forproper operation of relays of the type referred to.

It is therefore an object of this invention to provide a circuit bywhich successive pulses of fixed duration can be supplied to a loaddevice.

Another object is to provide a circuit by which successive pulses ofconstant duration can be supplied to a load regardless of significantvariations in source voltage.

A further object is to provide such a device in which the source voltagemay vary over a range limited only by the characterstics of the loaddevice, and within which range the load device will be provided withpulses each of constant, predetermined duration.

The invention employs a single power transfer element controlled bystart and stop impulses, the start impulses being provided by externalmeans, and the stop impulses being provided by a timing circuit. Thetiming circuit operation is also initiated by the start impulse, and iseffective to supply the stop pulse a predetermined time later than thenext preceding start pulse, in a manner substantially independent ofsupply voltage variation. The timing circuit employs a multi-elementsemiconductor device, such as a silicon controlled switch or a siliconcontrolled rectifier, which is responsive to two voltages to provide thestop pulse. One of the two voltages varies directly with changes insupply voltage, and the other varies inversely with changes in supplyvoltage. These two effects tend to cancel, holding the time delayconstant.

In order that the manner in which the foregoing and other objects areattained in accordance with the invention can be understood in detail, aparticularly advantageous embodiment of the invention will be describedwith reference to the accompanying drawings, which form a part of thisspecification, and wherein:

FIG. 1 is a schematic diagram showing one advantageous embodiment of theinvention; and

FIGS. 2A-D illustrate waveforms occurring at various points in thecircuit of FIG. 1.

Referring now to the drawings, it will be seen that an electromagneticrelay, indicated generally at 1, is shown as the load device to beenergized, one terminal of the relay coil being'connected to ground andthe other terminal being connected to the cathode of a siliconcontrolled switch (SCS) 2, and also to the cathode of a semiconductordiode 7. The cathode gate of the SCS is connected to a start input pulseterminal 3, and the anode of the SCS is connected to a positive D.C.supply terminal 4. The anode gate of the SCS is connected to oneterminal of a resistor 14 and also to one terminal of capacitor 15. Theother terminal of capacitor 15 is connected to resistor 5 and thecathode of a second SCS 6. The other terminal of resistor 5 is connectedto ground. The other terminal of resistor 14 is connected to positiveD.C. supply terminal 4. The anode of SCS 6 is connected to one terminalof a resistor S, and also to the anode of diode 7, the cathode of asecond diode 9, and to one terminal of a capacitance 10. The otherterminal of capacitance 10 and the anode of diode 9 are connected toground. The other terminal of resistor 8 is connected to positive D.C.supply terminal 4. The anode gate of SCS 6 is connected to one terminalof each of two resistors 11 and 12, the other terminal of resistor 11being connected to positive D.C. supply terminal 4, and the otherterminal of resistor 12 being connected to ground.

No connection is made to the cathode gate of SCS 6. It will be obviousto those skilled in the art that a unijunction transistor (UJT) could beemployed in place of the SCS 6, the SCS being advantageous because ofits superior switching characterstics.

Before operation of the subject circuit commences, SCS 2 and SCS 6 areboth in their nonconductive states, and the capacitance 10 is held at astate of essentially Zero charge by the clamping action of diode 7through the relatively low D.C. resistor of the load 1. Capacitor 15 ischarged via resistors 14 and 5 with the polarity shown. Operation isinitiated by the application of a start pulse to terminal 3, the startpulse being of positive polarity and of relatively short duration. Thestart pulse is shown at FIG. 2A, the assumption being made at this pointthat the maximum amplitude of the start pulse applied is just suflicientto cause SCS 2 to go into its high conduction state, the sequence ofoperation initiatingwhen the start pulse reaches that peak.

When SCS 2 begins to conduct, power will be supplied immediately torelay 1, the current flowing through the circuit formed by positive D.C.supply terminal 4, SCS 2, and the coil of relay 1 to ground beinglimited almost exclusively by the impedance of relay 1, the impedance ofSCS 2 being substantially zero when that device is in its highconduction state. The voltage at junction 13, and therefore at thecathode of diode 7, will then increase nearly to the level of thepositive D.C. source, this action being illustrated in FIG. 2C at theleading edge 20 of the pulse shown therein. Diode 7 will then berendered nonconductive, and capacitor 10 will commence charging throughthe circuit from the positive D.C. supply terminal 4 through resistor 8and capacitor 10 to ground. Capacitor 10 will charge in a period of timedetermined by the product of the values of resistor 8 and capacitor 10,this charge being represented by the curved portion 9 of FIG. 2B.

The voltage divider network formed by resistors 11 and 12 acts to holdthe anode gate of SCS 6 at a relatively constant voltage level, assumingthat the positive D.C. supply voltage remains constant, this referencevoltage level being shown at FIG. 2B by the dotted line 16. When thecharge across capacitance 10 increases to such a value that the voltageat the junction of resistor 8 and capacitance -10, this junction alsobeing connected to the anode of SCS 6, reaches a level above that atwhich the anode gate of SCS 6 is held as indicated by line 16 of 3 FIG.2B, SCS 6 will go into its highly conductive state, thereby dischargingcapacitor 10 very rapidly as indicated by portion 17 of the Waveformdiagram of FIG. 2B. The voltage across C at this instant is indicated asV High current will then flow from DC. supply terminal 4, and throughthe circuit including resistor 8, SCS 6, and resistor 5 to ground, andalso from capacitor 10, discharging through SCS 6 and resistor 5 toground. This positive pulse passes through capacitor 15, thereby raisingthe voltage level at the anode gate of SCS 2 above the voltage at theanode of SCS 2 by an amount V for a short period of time, as shown inFIG. 2D. This short duration high voltage pulse will act to turn SCS 2off, thereby terminating the current supply to the load device 1, asindicated by portion 18 of the Waveform diagram of FIG. 2C.

Diode 9 is inserted to absorb any inductive kickback from the loaddevice, thereby preventing capacitor 10 from accumulating a negativecharge.

As briefly described above, the duration of the pulse supplied to relay1, represented by the space between portions 14 and 18 of the waveformdiagram of FIG. 2C, is essentially independent of variations in the DC.supply voltage over a considerable range, including the intendedoperating voltage range for the relay 1. It will be clear that theperiod of time required for capacitor 10 to charge to a level sufiicientto initiate the turn-ofi pulse by placing SCS 6 in its conductive statewill change with variation in the DO. supply voltage. That is, as theD.C. supply voltage provided to terminal 4 decreases, the time requiredfor the voltage to traverse waveform portion 15, FIG. 2B, and to reach apredetermined voltage level will increase. However, it will also be seenthat, by the action of the voltage divider circuit including resistors11 and 12, as the voltage .at DC. supply terminal decreases, the voltagereference level at the anode gate of SCS 6 similarly decreases, therebyeffectively lowering the dotted line 1 6 in FIG. 2B, i.e., the voltagenecessary to cause SCS 6 to conduct. These two changes tend tocounteract each other, and effectively mantain constant the period oftime between the initiation of the charging cycle of capacitor 10 andits discharge. The time period between the waveform portions of FIG. 2Cindicated at 14 and 18, and representing the width of the pulse suppliedto the load device, therefore remains essentially constant.

As the DC. voltage supplied to terminal 4 is decreased, a point will bereached below which the system will not operate, simply becausesufficient potentials will not be present to cause the siliconcontrolled switches to go into their conductive states. However, it willfurther be seen that proper silicon controlled switches and theresistors 8, 11 and 12 and capacitor 10 can be selected by one skilledin the art for any nominal value of DC. voltage as required by theparticular relay used which will permit continued reliable operationwithout the need for special regulation of the DC. voltage supply. Ingeneral, electromagnetic relays are characterized by maximum and minimumcurrent requirements, and also by a pulse width requirement, the pulseWidth requirement being especially applicable to the more complex relaydevices such as stepping switches and the like. Thus, given a relayhaving particular characteristics, to apply the subject invention thedesigner need only select the proper ones of commercially availablesilicon controlled switches and a nominal middle value of DC. supplyvoltage. The circuit will then provide the desired reliability in pulseduration over considerable variation of the supply voltage from themiddle value selected, obviating the need for a regulated power supply.

Though one particularly advantageous embodiment of the invention hasbeen chosen for illustrative purposes, it will be clear that variouschanges and modifications can be made therein without departing from thescope of the invention as defined in the appended claims.

4 What is claimed is: 1. In apparatus for providing pulses of constantduration to a relay, the combination of a terminal to which unregulatedpositive DC voltage can be supplied, first circuit means having a firstcontrol terminal, a

second control terminal, and an output terminal,

said circuit means being operative to provide at said output terminal ofsaid first circuit means an electrical pulse of a duration dependentupon the time between application of a start pulse to said first controlterminal and a stop pulse to said second control terminal; capacitivecircuit means; charging circuit means; means for preventing operation ofsaid charging circuit means until a start pulse is applied to said firstcontrol terminal of said first circuit means; second circuit meansoperative to provide a reference voltage proportional to said positiveD.C. supply voltage; and means responsive to charging of said capacitivecircuit means to a predetermined voltage level and to said referencevoltage provided by said second circuit means for supplying a stop pulseto said second control terminal,

said last mentioned means being operative to provide said stop pulse ata fixed time later than the next preceding start pulse when said D.C.supply voltage is within a predetermined range. 2. In an apparatus forsupplying a pulse of predetermined duration to a relay device toenergize the same, the combination of first switching means having an ONstate and an OFF state and including a first control terminal to which acommand pulse can be supplied, a second control terminal to which a stoppulse can be supplied, and an output terminal to which the relay deviceto be energized can be connected, said first switching means beingoperative to convert to its ON state in response to a command pulsesupplied to said first control terminal and to convert to its OFF stateupon application of a stop pulse to said second control terminal; andtiming circuit means comprising second switching means, a capacitor,charging circuit means connected to said capacitor,

and clamping circuit means connected to prevent charging of saidcapacitor by said charging circuit means until a command pulse has beensupplied to said first control terminal of said first switching means,said second switching means being connected to discharge said capacitorat a predetermined time after supply of the command pulse to said firstcontrol terminal of said first switching means, said timing circuitmeans being connected to supply a stop pulse to said second controlterminal of said first switching means upon such discharge. 3. In adevice of the type described, the combination of an electromagneticrelay device; first controlled asymmetrically conductive circuit meanshaving a conductive state and a nonconductive state, said firstcontrolled asymmetrically conductive circuit means 'being connected toenergize said electromagnetic relay device when conductive; secondcontrolled asymmetrically conductive circuit means having a conductivestate and a nonconductive state;

first circuit means operative to render said first controlledasymmetrically conductive circuit means nonconductive when said secondcontrolled asymmetrically conductive circuit means conducts; capacitivecircuit means connected to be charged when said first controlledasymmetrically conductive circuit means is conductive; second circuitmeans for providing a reference voltage for said second controlledasymmetrically conductive circuit means; and third circuit means forimpressing the voltage level at said capacitive circuit means on saidsecond controlled asymmetrically conductive circuit means,

said second controlled asymmetrically conductive circuit means beingoperative to conduct when said volt-age level of said capacitor circuitmeans exceeds said reference voltage level provided by said secondcircuit means. 4. A relay energizing circuit comprising the combinationof a first semiconductor switching device having a conductive state anda nonconductive state, and including an anode, a cathode, a firstcontrol electrode and a second control electrode; v an input terminal towhich successive start pulses can be supplied,

said input terminal being connected to said first control electrode ofsaid first semiconductor switching device, said first semiconductorswitching device being rendered conductive when each of said pulses isapplied to said first control electrode thereof; a second semiconductorswitching device having a conductive state and a nonconductive state,and including an anode, a cathode and a control electrode; first circuitmeans connecting said cathode of said second semiconductor switchingdevice to said second control electrode of said first semiconductorswitching device, said first circuit means being operative to rendersaid first semiconductor switching device nonconductive when said secondsemiconductor switching device is conductive; a supply terminalconnectable to a source of positive DC. voltage; voltage divider meansconnected to said supply terminal for providing a reference voltagewhich is a substantially constant proportion of the voltage at saidsupply terminal,

said voltage divider means being connected to said control electrode ofsaid second semiconductor switching device; a capacitor; a chargingcircuitfor said capacitor; second circuit means connecting said anode ofsaid second semiconductor switching device to said capacitor and saidcharging circuit and operative to impress the voltage level of saidcapacitor on said anode of said second semiconductor switching device;first asymmetrically conductive circuit means connected to said cathodeof said first semiconductor switching device and to said capacitor,

said first asymmetrically conductive circuit means being operative tohold said capacitor in a state of substantially no charge when saidfirst semiconductor switching means is in a nonconductive state, and toelectrically isolate said capacitor from said first semiconductorswitching device when said first semiconductor switching device is in aconductive state;

a circuit portion for connecting a relay in series in the anode-cathodecircuit of said first semiconductor switching device;

said capacitor being operative to accumulate a charge when said firstsemiconductor switching device is in a conductive state; and

said second semiconductor switching device being rendered conductivewhen said capacitor accumulates a charge sufiicient to raise the voltagelevel of said anode of said second semiconductor switching device abovesaid relatively constant voltage level at said control electrode of saidsecond semiconductor switching device.

5. In a device of the type described, the combination of anelectromagnetic relay energizable by an electrical pulse ofpredetermined width and within a predetermined range of magnitude;

a first semiconductor switching device connected in series circuitrelationship with said relay, and having a first control electrode towhich a start command pulse can be applied, and

a second control electrode to which a stop comcommand pulse can beapplied,

said first semiconductor switching device being operative to convert toa condition of substantially zero impedance when a start command pulseis applied to said first control electrode;

a terminal connectable to a source of variable D.C.

' voltage predetermined range of magnitude for supplying voltage to theseries circuit of said relay and said first semiconductor switchingdevice;

a second semiconductor switching device having an anode, a cathode and acontrol electrode;

a voltage divider circuit for providing a reference voltage to saidcontrol electrode of said second semiconductor switching device,

said reference voltage being a substantially fixed proportion of thevoltage at said terminal and which varies in direct proportion to saidvoltage;

a capacitor; and

a charging circuit connected for charging said capacitor to the level ofsaid reference voltage in a period of time substantially equal to thewidth of said electrical pulse when said voltage supplied to saidterminal is within said predetermined range of magnitude.

References Cited by the Examiner UNITED STATES PATENTS 7/1965 Orsino317l48.5 9/1966 Schreiner 307-88.5

1. IN APPARATUS FOR PROVIDING PULSES OF CONSTANT DURATION TO A RELAY, THE COMBINATION OF A TERMINAL TO WHICH UNREGULATED POSITIVE D.C. VOLTAGE CAN BE SUPPLIED, FIRST CIRCUIT MEANS HAVING A FIRST CONTROL TERMINAL, A SECOND CONTROL TERMINAL, AND AN OUTPUT TERMINAL, SAID CIRCUIT MEANS BEING OPERATIVE TO PROVIDE AT SAID OUTPUT TERMINAL OF SAID FIRST CIRCUIT MEANS AN ELECTRICAL PULSE OF A DURATION DEPENDENT UPON THE TIME BETWEEN APPLICATION OF A START PULSE TO SAID FIRST CONTROL TERMINAL AND A STOP PULSE TO SAID SECOND CONTROL TERMINAL; CAPACITIVE CIRCUIT MEANS; CHARGING CIRCUIT MEANS; MEANS FOR PREVENTING OPERATION OF SAID CHARGING CIRCUIT MEANS UNTIL A START PULSE IS APPLIED TO SAID FIRST CONTROL TERMINAL OF SAID FIRST CIRCUIT MEANS; SECOND CIRCUIT MEANS OPERATIVE TO PROVIDE A REFERENCE VOLTAGE PROPORTIONAL TO SAID POSITIVE D.C. SUPPLY VOLTAGE; AND MEANS RESPONSIVE TO CHARGING OF SAID CAPACITIVE CIRCUIT MEANS TO A PREDETERMINED VOLTAGE LEVEL AND TO SAID REFERENCE VOLTAGE PROVIDED BY SAID SECOND CIRCUIT MEANS FOR SUPPLYING A STOP PULSE TO SAID SECOND CONTROL TERMINAL, SAID LAST MENTIONED MEANS BEING OPERATIVE TO PROVIDE SAID STOP PULSE AT A FIXED TIME LATER THAN THE NEXT PRECEDING START PULSE WHEN SAID D.C. SUPPLY VOLTAGE IS WITHIN A PREDETERMINED RANGE. 